1. Field of the Invention
The present invention relates to a semiconductor device, communication device, and a method of inspecting a semiconductor device.
2. Related Background Art
Along with the movement toward low-power-consuming mobile communication devices for two-way communications of high-frequency (also referred to as “radio-frequency” or “RF” hereunder wherever appropriate) signals, there is a demand to reduce the insertion loss of a high-frequency (RF) switch circuit provided between an antenna and transmission/reception circuit or between an antenna and a reception circuit and to reduce the power consumption of the switch circuit itself. On this account, the switching element should preferably be of a lower insertion-loss type that needs no DC bias current, like a diode. Currently, HEMT (high electron mobility transistor), one of the high-performance FETs (field effect transistors), is employed as this type of switching element because a high-frequency switch circuit composed of an HEMT consumes little power and exhibits high isolation properties and small insertion loss. Currently available high-frequency switch circuits are shunt-type ones and resonant-type ones (see JP-H06-152361-A).
FIG. 13 is a circuit diagram of a typical conventional shunt-type SPST (single-pole single-throw) switch circuit. This shunt-type switch circuit includes two FETs (simply called “transistors” hereunder) T1 and T2 to switch RF signals. In pre-shipment inspection of a product including the shunt-type switch, the transistors T1 and T2 are normally checked in terms of DC (direct current) characteristic to judge acceptability of the transistors T1 and T2. This is because transistors, in general, including those used with RF signals, can be verified for acceptability by inspection of DC characteristics without inspection of RF characteristics.
FIG. 14 is a circuit diagram of a typical conventional resonant-type SPST switch circuit. The resonant-type switch circuit includes a transistor T3 as a switching element, and an inductor L1 connected in parallel to the transistor T3. Resonant-type switch circuits, in general, are superior to shunt-type switch circuits in isolation property for RF signals.
However, pre-shipment inspection of products including resonant-type switch circuits cannot check DC characteristics of the transistor T3 because the inductor L1 connected between the source and drain of the transistor T3 makes a short-circuit for DC current between the source and the drain. Therefore, in pre-shipment inspection of products including resonant-type switch circuits, the resonant circuit composed of the transistor T3 and the inductor L1 must be inspected in terms of RF characteristics in order to judge the acceptability of the transistor T3. This means that an inspection apparatus dedicated to checking RF characteristics must be used in the inspection process. Accordingly, it has been a problem that inspection of products including resonant-type switch circuits is more expensive than inspection of products including shunt-type switch circuits.